When a hole or a trench is formed with a high aspect ratio by performing a plasma etching process on an oxide film made of an oxide such as silicon dioxide, a fluorocarbon-based gas or a particle fluorocarbon-based gas which easily generates a reactive product is used (see, for example, Japanese Patent Application Laid-Open No. 2009-206444). The generated reactive product is deposited on a mask layer or an inner surface of the hole or trench, but the reactive product deposited on the mask layer suppresses etching of the mask layer and thus contributes to improving a selection ratio of the oxide film to the mask layer in etching. The reactive product deposited on the inner surface of the hole or trench, in particular, the side of the hole or trench suppresses etching of the side to prevent bowing, which is a phenomenon in which a cross-sectional shape of the hole or trench is expanded, from being generated.
However, when the high aspect ratio hole or trench is formed by the plasma etching, the duration of the plasma etching becomes longer, and as a result, the amount of the generated reactive product increases until the end of plasma etching process. When the amount of the generated reactive product increases, the amount of the reactive product deposited on the bottom of the hole or trench also increases, and as a result, etching of the hole or trench is impeded in the end of plasma etching time, thereby deteriorating an etching rate.